Roasting furnace



July 2`, 1935. F JOHANNSEN 2,007,121 RoAsTING FURNACE Y Filed Feb'. 9, 1954 171,7, balomc l l ofundesi ble conshfuens l f Friedrich Johansen Patented July 2, 1935 v 2,007,121 noAfsTlNG FURNAQE Friedrich Johannsen, Magdeburg, Germany Application February 9, 1934, Serial No. 710,511

In Germany February 15, 1933 7 Claims.

My invention relates to the problem of roasting exhaustively and under conditions of economy zinc-blend and other' ores, which contain sulfur, arsenic, antimony,

which because of their liability to frit and coalesce at relatively low temperatures and because of other adverse conditions, known to practitioners, are dicult in practice to be thoroughly desulfurized and completely roasted in metallurgi- 10 cal furnaces of known design including those of the rotary tubular types.

It has been attempted by the inventor to roast zinc blend in a rotary tubular furnace of theordinary single'chamber'type by causing the charge to pass through the furnace in an unusually thick layer so as not too frequently come into contact with the oxidizing'air, in order to prevent a' too rapid and violent combustion of the sulfur in the charge and thus to avoid the production of excessive heat.

'Ihe results however have been unsatisfactory inasmuch as, afterlthe bulk of.. the *sulfur has been burnt in the middle section of the furnace,

the sulfur content retained in the charge, while the latter proceeds towards the exit of the furnace gradually becomes inadequate for being kept burning. In other, words: The relatively small balance of the sulfur-about-l-7%-can not be burnt because of the very thickness of the 3o layer of the charge and its inadequate contact with the oxidizing air. Y

' Moreover additional heat from without in the f orm of combustion gases Acarrying with them an excess of air cannot be applied to the charge appreaching the exitofthe furnace, because the sulfurous acid issuing from fthe furnace, which it is compulsory by law to collect in-Germany and other countries, is mostly used forthevproduction of sulfuric acid and therefore must be 40 kept free from contamination with carbonio acid and nitrogen of which `are composed:-

Further efforts and suggestions made byother inventors how to re`design the single chamber rotary tubular furnace so as to convertit into an efficient roasting furnace, from which an exhaustively roasted product is obtained, which l should-be entirely free from sulfur, include the provision of anv expansion chamber, of air pipe the said combustion gases systems, automatic valvesfour way cocks-air ducts, scoops etc. for the timely introduction of air into different sections of the furnace, as described for instance in the U. S. Letters Patent 1,791,403 and 1,830,002.

etc. in varying quantities, and.

The invention disclosed hereinafter also aims at overcoming the aforesaid difficulties by providing for the specific purpose of exhaustively roasting zinc-blend andother materials of the character described-a structurally improved rotary tubular furnace of relatively simpledesignf- 5 which can beerected andoperated at relatively low cost, being distinguished from roasting furnaces used or proposed heretofore by the absence of any complicated, moveable and costly accessorial parts. v

In connection therewith the invention aims at so re-designing a rotary tubular furnace of the single chamber type for the purposes indicatedl that its manner of working, viz. the heat produced and the reactions occurring in its different sections or zones can be easily controlled, modied and adapted at short notice to varying conditions brought about foi` instance by accidental changes in the sulfur or iron content of the ore etc., so as to ensure a complete desulfurization of the material under treatment.

. r,Other objects involved in this invention will become incidentally apparent hereinafter to practitioners 1n this field.

' 'I'he nature and scope of the invention are briey outlined in the appended claims and will be more fully understood from the following specicatlon taken:v together with the accompanying drawing in which f a rotary shell S open at'both ends, which is 4lined with refractory material and is subdivided at its 'lower end for a portion of its length' into a plurality of chambers for the detail hereinafter.

'I'he furnace is preferablymounted at a small angle of inclination-ranging about 1% p ercent-so as .to enable the charge t0 pass, While purpose described in 45 the furnace'rotates at a moderate rate .of speed, 50

in .a relatively thick layer L through the single chamber sections A', B of the furnace.v 'I'he total length of said sections A, B is so chosen, vthat the charge, while passing through section A is gradually. heated up to the point of inflamma- 55 tion by the hot combustion gases produced in section B, in which the bulk-of the sulfur and other combustible matter in the charge is burnt.

Feeding means F are provided at the upper end of the furnace for delivering the charge into the single chamber section A.

One of the most salient features of, the invention consists therein, that the furnace is longitudinally subdivided at its lower end for a portion of its length into a plurality of chambers, collectively hereinafter called multiple-chamber section, and being designated C, which is preferably in direct and open communication with the single chamber section B.

As seen in Fig. 1 by the provision of a plurality of chambers in section C of thefurnace the charge, which has passed through sections A, B in a relatively thicklayer L, is split up into a number of smaller currents of smaller thickness with the result, that a larger surfafe of the charge than before is exposed to the oxidizing air, whereby the charge, being trundled around and agitated, is more frequently and intimately brought into contact with the air. As the sulphur content has already been materially reduced in the main roasting zone B, the danger of the charge getting overheated in the final roasting zone C, which would occur if the preliminary and main roasting zones A, B were of like formation, is avoided. 1

' The inventors experimental work has shown, that the best results are obtained, if the length of the multiple chamber section C does not exceed one third of the total length of the furnace, and that the charge is capable of ridding itself in the final roasting zone from all the balance of sulfur, arsenic and other undesirable constituents.

According to this invention means are provided enabling the operator to control the heat developed and the reactions occurring in the furnace, so as to ensure its steady operation and a substantially uniform quality of the roasted product.

In their preferred embodiment said heat controlling means comprise (1) An air duct D, axially extending through the central portion of the multiple chamber section C, and an air pipe P, which is conveniently provided with ,a valve and is connected with a fan, not shown, by which cold or preheated airaccording to requirementscan be blown directly into the'single chamber section B of the furnace,

(2) Burners U, U2 for the admission of gaseous, liquid or pulverulent-fuel, by which the fuihace is heated up on being set into operation, and by which in cases of emergency additional heat can be applied to the charge;

(3) Instead of providing burners U, U2, hot airif available-may be conveniently introduced into the furnace through an airconduit T leading into the hood H, which encloses the exit end of the furnace.

Various other changes and modifications may be made in the design and structural details of roasting furnaces of the improved type described hereinbefore, without departingfrom the spirit and the salient ideas of thisinvention:

As seen in Figs. 3 and 4 the outer walls of the chambers'of the final roasting zone C may be provided with extra thick or additional linings i, i2 with the object ofi materially reducing the aggregate diameter of the chambers in the nal roasting zone C and thus forming a step or baille ring, in front of which the charge is dammed up andis collected in a thick layer; this simple expedient allows of re-constructing and using to equal advantage rotary tubular furnaces for the purposes of this invention which are mounted at a steeper angle than 11/2 percent, specified above.

Instead of chambers having a cross sectional shape of a sector-shown in Figs. 2, 3, 5-circular or oval shaped chambers o, o2 shown in Fig. 4. may be conveniently used in the final roasting zone C.

Chambers of circular cross sectional shape o have been found to be preferable in cases, where the ores under treatment tend to become overheated during the roasting process.

Instead of four or five chambers, shown in the drawing, any other convenient number may be provided in the multiple chamber section C of the furnace consistent with the diameter of the latter and the nature of the material to be roasted.

Oxidizing air instead of being blown into the furnace through air duct D may be conveniently drawn thereinto by natural or suction draft.

Good results have beenmbtained in practice with a tubular rotary furnace designed according to this invention for roasting flotation zincblend, the granules of which would pass through a sieve having 60 meshes; the diameter of the outer shell of the furnace being about 2 meters, its total length 20 m., the length of the multiple chamber section 5 m.; the thickness of the refractory lining in the single chamber section being mm. and of that in' the multiple chamber section 300 mm.; the latter containing 6 cham"- bers.

What I claim iszl. In a tubular rotary furnace for roasting ores, the combination with a shell having a lining of refractory material and presenting a single chamber section at the intake end of the furnace, of a multiple chamber section formed at the outlet end of the furnace, and means for separately introducing reaction agents into the multiple and the single chamber sections of the furnace from the outlet end of the latter.

2. In a tubular rotary furnace for roasting ores, the combination with a shell having a lining of refractory material and presenting a single chamber section at the intake end of the furnace, of a multiple chamber section formed at the outlet end of the furnace, and means for separately introducing reaction agents into the multiple and the single chamber sections of the furnace from the outlet end of the latter, said means comprising a hood enclosing the outlet end of the furnace, an air duct and pipes cooperatively associated with said hood for feeding reaction agents into the multiple chamber section of the furnace and another air duct longitudinally extending through the multiple chamber section for feeding reaction agents into the single chamber section.

3. In a tubular rotary furnace for roasting ores, the combination with a substantially cylindrical shell having a lining of refractory material and presenting a single chamber section at the intake end ofthe furnace, of a multiple chamber section formed at the outlet end of the fin'naee, and means for damming up the charge in front of the multiple chamber section.

4. In a tubular rotary furnace for roasting ores,

the combination with a substantially cylindrical shell having a lining of refractory material and presenting a single chamber section at the intake end of the furnace, of a multiple chamber section formed at the outlet end of the furnace, and means for damming up the charge in front of themultiple chamber section,- said means comprising re- `fractory linings which are of greater thickness in the 'multiple chamber section than in the single chamber section of the furnace.

5. In a tubular rotary furnace for roasting ores, a rotary shell having a single `chamber zone within which the ore is initially treated for removing the major portion of the undesirable constituents, a plurality of separate chambers arranged in the outlet zone of the shell for receiving the previously treated ore from the single chamber so that an increased contact is effected between the charges in theseparate chambers with air and reaction agents, means for supplying the ore to be treated into the single chamber zone, a hood the interior of vwhich is in permanent communication with all of the separate chambers, and which has means for supplying air into the hood. and means for supplying reaction agents into the hood.

6. In a tubular rotary furnace for roasting ores, a rotary shell having a single chamber zone within which the `ore is initially treated for removing the major portion of the undesirable constituents, a plurality of separate chambers arranged in the outlet zone of the shell for receiving the Ipreviously treated ore from the single chamber so that an increased contact is eiected between the charges inthe separate chambers with air and reaction agents, means for supplying the ore to be treated into the single chamber zone, a-hood the interior of'which is in permanent communication with all of the separate chambers and which has means for supplying into the hood air and `other reaction agents.

'1. In a tubular rotary furnace for roasting ores, a rotary shell having a single chamber `zone within which the ore is initially treated for removing the major portion of the undesirable constituents, a plurality of separate chambers arranged in the outlet zone oi' the shell for receiving the previously treated ore from the single chamber so that ,an increased contact is effected between the charges in the separate chambers with air and reaction agents, means for supplying the ore to be treated into the ,single chamber zone, a hood the interior of which is in permanent communication with all of the separate chambers and which has means for supplying/into the hood air and other reaction agents, and means extending through the outlet zone of the shell and separate from the plurality of separate chambers for supplying air into the single chamber zone oi the furnace.

FRIEDRICH JOHAN'NSEN. 

